1. Field of the Invention
The present invention relates to an image forming apparatus, and in particular, to an improvement of a feeding mechanism which feeds sheet material one-by-one.
2. Description of the Related Art
In an electrophotographic image forming apparatus, a paper feeding roller (a pick-up roller) which makes a contact with an uppermost sheet material among the stacked sheet material, is provided for feeding the sheet material one-by-one. For feeding the sheet material one-by-one, it is important that the paper feeding roller is pressed against the sheet material with a predetermined thrust. Incidentally, since the sheet material is consumed one-by-one as the image formation goes on, a position of the uppermost sheet material goes on changing gradually. Therefore, a moving mechanism which moves the sheet material and the paper feeding roller depending on the position variation of the sheet material with the consumption of the sheet material is necessary for keeping a constant pressure of the paper feeding roller against the sheet material.
An image forming apparatus described in Japanese Patent Application Laid-open No. 2007-269462, includes a driving-force transmitting mechanism which transmits a driving force for lifting up a pressing plate (loading plate) in a paper supply tray. Moreover, the driving-force transmitting mechanism has a one-way clutch which regulates a downward displacement of the pressing plate. In other words, the one-way clutch is used such that even when the driving force is not applied to the pressing plate, the pressing plate does not move downward by a weight of recording sheets mounted on the pressing plate.